Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>
Here's a link to the scanned Lindsay booklet pages covering rotary phase
converters:
http://www.tesla-coil-dot-com/images/images/RotaryPhaseConverter1.jpg
John
---------- Original Message ----------------------------------
From: "Tesla list" <tesla-at-pupman-dot-com>
Date: Sat, 03 Apr 2004 10:12:09 -0700
>Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
>
>
> > The gadgets described are capacitor-start arrangments for the three
> > phase motor, generating enough torque to get it running after which it
> > runs on a single phase with accordingly reduced power. On inspection
> > they contain a large ELECTROLYTIC starting capacitor, a resistor, and a
> > relay. I assume the Lindsay book gives construction details. Both my
> > lathe and my mill have three-phase motors which I run this way and they
> > are noticeably deficient in torque. There is another technique which is
> > sometimes used, but not at all convenient. A large three-phase motor is
> > started single phase that way and, once it's running three phase power
> > can be drawn from its three connections, only two of which are connected
> > to the single phase input line. No magic really, the three-phase motor
> > is operating as a three-phase induction generator. Cumbersome and not
> > very efficient, but can be used.
> >
>
>I don't know that it's all that inefficient, compared to other ways of
>making three phases from one (Motor generator, solid state inverter).. the
>rotary converter DOES depend on the load being reasonably balanced.
>
>The other thing is that the 3phase motor being used has to be sized
>appropriately. I seem to recall a rule of thumb that the motor has to be
>twice the size of the load (i.e. If you want to run a 2 HP three phase load,
>you'll need a 5HP three phase motor for the converter).. probably has to do
>with the current in the windings.
>
> They also make specialized devices for this application with somewhat
>different rotor design and stator windings (I don't know that the wining for
>the stator uses different gauges on the line and load windings, or, even, 4
>windings). Certainly, the rotor design can be optimized from the usual
>induction motor rotor designs (which are tailored to give the desired torque
>vs speed curves, depending on the mechanical load characteristics. A
>compressor or a punch press is a very different load than a fan)
>
>
>